Lubricating oil process



Dec. 21, 1965 A. P. ANDERSON 3,224,955

LUBRIGATING OIL PROCESS Filed D60. 18, 1962 PARAFFINIC LUBRICAT ING OILDISTILLATE SOLVENT EXT "AROMATIC EXTRACT RAFFINATE OF LESS THAN 8% WPOLYAROMATICS DEWAXING WAX DEWAXED OIL MILD HYDROGENATION ADSORBENTTREATMENT V REFRIGERATER OIL HIS ATTORNEY United States Patent 3,224,955LUERICATING OltL PROCESS Alvin P. Anderson, Woodcliif Lake, N.J.,assignor to Shell Oil Company, New York, N.Y., a corporation ofDeliaware Filed Dec. 18, 1962, Ser. No. 245,384 5 Claims. (Cl. 208-28)This invention relates to a process for preparing lubricating oils andmore particularly it relates to a process for preparing lubricating oilsfor refrigeration units.

Refrigerators, food freezers, air conditioners and the like, exceptthose that are motorless, have compressors which compress therefrigerant. The most commonly used refrigerants are those which areimmiscible with the lubricant, such as ammonia. sulfur dioxide and thelike and those which are miscible with the lubricant, such as halogentype, for example, methylchloride and chlorofluoro carbons (Preons). TheFreons, such as Freon 12 (dichloro-difluoro methane), have become widelyused in the industry.

When refrigeration units are assembled, the lubricating oil ishermetically sealed inside the equipment. Here it is in contact with therefrigerant and the metals and other materials of construction duringthe life of the mechanism. As the totally enclosed units are to providea satisfactory service for a long period of time, the lubricant shouldbe oxidation stable, non-sludging and non-corrosive. The oil should besuffiicently soluble in liquid Freon to properly lubricate thecompressor bearings and other moving parts. In addition, the oil carriedover to the low temperature side of the unit should not separate andcoat heat exchange surfaces or plug restrictor valves. In the hightemperature, high pressure Zone of the unit, the thermal stability ofthe oil-Freon mixtures in the presence of metal is of great concern.These performance characteristics are the most critical for therefrigerator oil.

Demand for refrigeraotr oils has been met by drastic refining oflubricating oils such as by severe acid treating and clay contacting.Such refining methods are highly expensive, present disposal andhandling problems, and generally result in a low yield of finished oil.

It has been found, in accordance with the present invention, thatsatisfactory refrigerator oils can be prepared by extracting minerallubricating oil distillate to a polyarornatic content less than about 8%by weight, mildly hydrotreating the lubricating oil raflinate todesulfurize the oil and then subjecting the hydrogenated oil to amoderate clay treatment. The drawing is a block flow diagram which setsforth operational steps in the practice of this invention.

The starting material is a straight-run mineral oil distiilate,preferably from a parafiinic type crude oil. Paraffinic oils producelubricating oils of high viscosity index (HVI) which are desired becauseof the extremes of temperatures at which a refrigerator oil mustfunction in service. The distillates are produced by fractionaldistillation, generally under vacuum, of the crude oil into fractions ofvarying viscosity (Saybolt Universal at 100 F.) and boiling ranges, suchas 100 distillate, 250 distillate, heavy (700) distillate, and shortresidue. The distillates are generally refined separately to providebase stocks which can be blended to give an oil of the desired finishedproperties.

3,224,955 Patented Dec. 21, 1965 The lubricating oil distillate startingmaterial is subjected to an aromatic extraction process with a solventselective for aromatics, such as furfural, S0 phenol and the like.Extraction is usually conducted at relatively low temperatures of about-200 F. and solvent to feed volumetric ratios of 0.5-5. Polyaromaticcontent of distillate fractions generally ranges from about 15- 30% byweight. In the process of the invention the extraction should be severeenough to reduce polyaromatic content of the raifinate to less thanabout 8% by weight, preferably less than 5% by weight, the extractionconditions employed to achieve this depth of extraction depending uponthe particular distillate feed and solvent used. Solvent extractionprocesses are well known and are practiced commercially, thereforedetailed discussion should not be required. Acidic solvents such asphenol are preferred as they tend to remove more of the basic nitrogencompounds from the lubricating oil distillates.

Extraction removes unstable constituents from the oil, primarilypolyaromatics and nitrogen, sulfur, and oxygen compounds, usually in anaromatic structure. Resistance of the oil towards oxidation and sludgingis improved. However, the presence of mono-aromatics in the oil isdesired to give the oil oxidation stability. By removing polyaromaticand introgen compounds, the extraction improves viscosity index of theoil and improves susceptability of the oil to oxidation inhibitors.

With paraffinic type crudes, dewaxing is required to remove Waxycomponents, which thereby improves the pour point of the oils.Ra'l'finate from the extraction process can be subiected to any suitabledewaxing operation. Dewaxing processes employed commercially employsolvents such as propane, methyl-ethyl-ketone (MEG/benzene, and thelike. Pour point of the dewaxed oil is preferably below about 10 F.Alternatively, dewaxing may precede solvent extraction.

The dewaxed rafiinate is subjected to a mild hydrodesulfurizationwherein sulfur and oxygen compounds are hydrogenated while thehydrocarbons remain substantially unaffected, i.e. virtually no crackingof the oil or hydrogenation of aromatics present in the oil. Viscosityindex of the oil may be slightly increased by the mild hydrotreatrnent.The oil may be in either the gas or the liquid phase duringhydrogenation, a very suitabie method being trickle phase hydrogenationwherein the liquid oil is caused to flow through a bed of catalyst inthe presence of hydrogen. in general, the hydrogenation is carried outat a temperature of 550 to 700 F a pressure of 450 to 1500 p.s.i.g., agas discharge rate of 250 1200 standard cubic feet of hydrogen perbarrel of oil, and a liquid hourly space velocity of about 1 to 4. Underthe mild conditions, hydrogen consumption will be about 20-250 standardcubic feet/barrel of oil and sulfur removal will be about 5075%complete. More severe hydrogenation, i.e. loW space velocities, highpressures and high temperatures, would increase sulfur and introgenremoval, hydrogenation of aromatics, and hydrogen con sumption, butwould be considerably more expensive.

Suitable hydrodesulfurization catalysts are oxygen or sulfur containingcompounds such as the oxides and the sulfides of metals of Group 6 andGroup 8 of the Periodic Table. Especially preferred are molybdenum oxidetogether with cobalt oxide and/or nickel oxide, or tungsten sulfide andnickel sulfide. The catalysts are preferably supported on a carrier suchas active carbon, kieselguhr,

silica, alumina, and the like. The catalyst may be used in the form oftablets, pellets, extrudates and the like. I-lydrodesulfurizationcatalysts are well known and many are available commercially. A suitablehydrogenation method is described, for example by Hoog, US. Patent2,608,521, issued August 26, 19 52.

In the hydrodesulfurization, a minor amount of low boiling components isproduced which results in a lowering of the flash point of the oil. Itmay be necessary to remove these low boiling components to satisfy flashpoint requirements of the finished oil. This can be done by means ofsteam-stripping or distillation, preferably under reduced pressure.

Following the hydrodesulfurization, the oil is moderately treated with asolid adsorbent such as fullers earth and activated clays. Commonadsorbents are for example attapulgite and montmorillonite and the acidactivated clays such as bentonite, bauxite and alumina. Suitableadsorbents are Porocel and Filtrol. The treatment can be efliected atelevated temperatures, for example, from about 200-500 F. When strippingof hydrodesulfurized oil is employed, it is generally desired to passthe stripped oil at normal stripper bottoms temperatures through apercolation filter containing the adsorbent. Contact filtering withmoderate clay dosages can be employed if desired. The quantity ofadsorbent used generally lies between 0.5 and by weight, preferablybetween 1 and 5% by weight, calculated on the oil treated. In practice,the various distillate fractions will often be blended in the desiredproportions prior to the adsorbent treatment.

Hydrodesulfurization of the oil results in a more effective adsorbenttreatment since sulfur and oxygen compounds are removed in thehydrotreating operation which would otherwise interfere by formingviscous residues on the adsorbent. Moreover, although little or nonitrogen compounds are removed in the hydrodesulfurization, thehydrotreatment apparently promotes nitrogen base formation resulting inincreased denitrification in adsorbent treatment.

Removal of traces of nitrogen compounds, particularly basic nitrogencompounds, is essential to obtain satisfactory chloride ion stabilitytest results for refrigerator oils. The chloride ion stability test isdesigned to stimulate conditions in service where oil, Freon andmaterials of construction are in contact with one another during theoperating life of the refrigerator unit. Test oil, Freon 12, steel andcopper in prescribed amounts are heated together in a sealed tube attest temperature, generally 400 F. After a given time the tube is cooledand opened and the oil is examined for sludge, color, and the amount ofchloride ion formed. A minimum of chloride ion is desirable sincechloride accelerates rusting, metal corrosion, and deterioration oforganic materials, e.g. insulation.

If desired, suitable additives such as oxidation inhibitors, anti-foamagents and the like can be incorporated in the treated oil to improvecharacteristics of the oil. The additives should be oil soluble andnon-sludge forming. Oxidation inhibitors such as the phenolic type, e.g.2,6- ditertiarybutyl-4-methylphenol, are preferred, since nitrogencompounds, such as the amine type, can adversely affect chloride-ionstability of the oil.

Viscosity of the final lubricating oil can be within a wide range,depending upon the particular service and preferences of therefrigeration unit manufacturer. Viscosity of lubricating oil inrefrigerator service is usually about 500 SSU at 100 F., although oilsof a viscosity as low as 80 SSU at 100 F. can be used if desired. Oilshaving a viscosity of 1000 SSU at 100 F. and higher are desired for airconditioning units. Viscosity index of the final oils is at least about85 and preferably at least 90.

EXAMPLE Long residue from the topping of lube crude is vacuum distilledinto 100 distillate, 250 distillate, heavy (700) dis- 4: tillate, andshort residue. The 250 and heavy distillates are extracted with phenol,solvent to feed volumetric ratio of about 1.2 and 2.4, respectively, andthe raffinates obtained are dewaxed with methyl-ethyl-ketone/toluene(app. 60% MEK, 40% toluene) at solvent to oil ratios of about 2.3 and3.5 respectively. Typical properties of the extracted and dewaxeddistillates are given in Table I.

Several blends of the dewaxed distillates were prepared, each blendcontaining about -85% w. heavy distillate and having a viscosity ofabout 500 SSU at F. A typical blend has the following aromatichydrocarbon content, by ultraviolet analysis (mol. wt. 510-520):

percent wt. Monoaromatics 9.8 Diaromatics 2.0

Triaromatics 0.3 Tetraaromatics 0.2

Thus, the polyaromatic content was about 2.5% wt. The various blendswere subjected to clay contacting or percolation with or without aprevious hydrotreatment over nickel molybdenum on alumina hydrogenationcatalyst. Nitrogen content and chloride ion test results are given belowin Table II. The chloride ion test Was determined on sample containing0.5% w. oxidation inhibitor (2,6-ditertiarybutyl-4-methylphenol) and 5p.p.m.

antifoam agent (Dow Corning Fluld, Type 200).

Table II Nitrogen, p.p.m. Chloride Ion after No. Treatment 2 Weeks TotalBasic at 400 F.

1 Untreated blend -1 31 11 2 Clay contacted, 30 lb. Filtrol 9 1 1088/bbl. 3 Percolated over Porocel at 210 F 27 2 147 4 Hydrotrcated 675F., 450 p.s.1.g.,

2.5 LHSV 34 11 425 5 IIydrotreated 675 F., 450 p.s

1.25 LHSV. 15 4 177 6 I-Iydrotreated 675 F., 550 p.s.i.g., 21 5 149 1.25LHSV. 7 N o. 4 percolatcd over Iorocel at 8 1 5. 2

210 F. 8 No. 4 clay contacted, 3011). Filtrol l0 1 3. 0

SS/bbl.

As shown in Table II, simple percolation (No. 3) of extracted anddexwaxed oil is far less effective than clay contacting (No. 2).Similarly, mild hydrotreatment is also ineffective (Nos. 4-6). However,mild hydrotreatment prior to clay treatment (Nos. 7-8) has markedlyimproved chloride ion test results. In addition, a comparison of numbers3 and 7 shows that hydrotreatment facilitates denitrification bypercolation clay treatment. The difierence in chloride-ion reactivity ofoils having a basic nitrogen content below the detectable level of 1p.p.m. is presumed to be related to the presence of pyrrole, indole, orcarbazole type compounds which are too weakly basic to be detected bythe perchloric acidacetic acid reagent used to measure basic nitrogencontent.

I claim as my invention:

1. A process for the production of refrigerator oil which comprisesextracting a paraflinic lubricating oil distillate with a solventselective for aromatics to obtain a ratfinate having a polyar-omaticcontent less than about 8% by weight, dewaxing the raffinate,catalytically hydrotreating the dewaxed raflinate under mild conditionsof about 550 to 700 F., about 450 to 1500 p. s.'i.g., and about 1 to 4liquid hourly space velocity, and contacting the hydrotreated oil with asolid adsorbent.

2. A process for the production of refrigerator oil which comprisesextracting a paraffinic lubricating oil distillate with a solventselective for aromatics to obtain a raffinate having a polyaromaticcontent less than about 8% by weight, dewaxing the raifinate,catalytically hydrotreating the dewaxed raffinate under mild conditionsof about 550 to 700 F., about 450 to 1500 p.s.i.g., and about 1 to 4liquid hourly space velocity, and percolating the hydrotreated oilthrough a solid adsorbent.

3. A process for the production of refrigerator oil which comprisesextracting a paraffinic lubricating oil distillate with a solventselective for aromatics to obtain a rafiinate having a polyaromaticcontent less than about 20 6 tacting the hydrotreated oil with betweenabout 0.5 and 10% by weight of a solid adsorbent.

4. A process for the production of refrigerator oil which comprisesextracting a parafiinic lubricating oil distillate with anacidic-solvent selective for aromatics to obtain a raflinate having apolyaromatic content less than about 8% by weight, dewaxing therafiinate, catalytically hydrotreating the dewaxed rafiinate under mildconditions of about 550 to 700 F., about 450 to 1500 p.s.i.g., and about1 to 4 liquid hourly space velocity, and contacting the hydrotreated oilwith a solid adsorbent.

5. The process according to claim 4 wherein the solvent is phenol.

References Cited by the Examiner UNITED STATES PATENTS 2,673,175 3/1954Stratford etal 208-48 2,967,144 '1/1961 C016 208--87 2,967,146 1/1961Manley 208-87 2,967,147 1/1961 C016 20s 1s DELBERT E. GANTZ, PrimaryExaminer.

ALPHONSO D. SULLIVAN, Examiner.

1. A PROCESS FOR THE PRODUCTION OF REFRIGERATOR OIL WHICH COMPRISESEXTRACTING A PARAFFINIC LUBRICATING OIL DISTILLATE WITH A SOLVENTSELECTIVE FOR AROMATICS TO OBTAIN A RAFFINATE HAVING A POLYAROMATICCONTENT LESS THAN ABOUT 8% BY WEIGHT, DEWAXING THE RAFFINATE,CATALYTICALLY HYDROTREATING THE DEWAXED RAFFINATE UNDER MILD CONDITIONSOF ABOUT 550* TO 700*F., ABOUT 450 TO 1500 P.S.I.G., AND ABOUT 1 TO 4LIQUID HOURLY SPACE VELOCITY, AND CONTACTING THE HYDROTREATED OIL WITH ASOLID ABSORBENT.